The Internet is a decentralized network of computers that can communicate with one another via a transmission control protocol/internet protocol (TCIP/IP). Although the Internet has its origins in a network created by the Advanced Research Project Agency (ARPA) in the 1960's, it has only recently become a worldwide communication medium. To a large extent, the explosive growth in use of the Internet is due to the development in the early 1990's of the worldwide Web (WWW), which is one of several service facilities provided on the Internet. Other facilities include a variety of communication services such as electronic mail, telnet, usenet newsgroups, internet relay chat (IRC), a variety of information search services such as WAIS and Archie, and a variety of information retrieval services such as FTP (file transfer protocol) and Gopher.
The WWW is a client-server-based facility that includes a number of servers (computers connected to the Internet) on which Web pages or files reside, as well as clients (Web browsers) which interface the users with the Web pages. Specifically, Web browsers and software applications such as WebExplorer.RTM. (IBM Corporation) or Navigator.RTM. (Netscape Communication Corporation) send a request over the WWW to a server requesting a Web page identified by a Uniform Resource Locator (URL) which notes both the server where the Web page resides and the file or files on that server which make up the Web page. The server then sends a copy of the requested file(s) to the Web browser, which in turn displays the Web page to the user.
The Web pages on the WWW may be hyper-media documents written in a standardized language called HyperText Markup Language (HTML). A typical Web page includes text together with embedded formatting commands, referred to as tags, which can be used to control font size, font style and the like. A Web browser parses the HTML script in order to display the text in accordance with the specified format.
Although many new computer applications are being developed for distributed processing environments such as the Web, there is still a large installed base of traditional computer systems having an architecture including a central host computer, typically a mainframe, and "dumb" computer terminals which are directly connected to ports of the host computer. Examples of such a configuration include IBM 3270, IBM 5250 and ASCII configurations in which a terminal communicates with a host according to a networking protocol such as TCP/IP. The networking protocol typically provides for structured grouping of data stream transmissions with a series of control characters followed by a block of displayable characters, a typical data stream comprising a plurality of sequentially transmitted control character blocks followed by displayable character blocks.
Because of the continued presence of such host-based applications, there is a need for techniques to integrate host-based content into the Web paradigm. For example, many companies have centralized information databases, services and the like, which are accessible to employees from terminals or personal computers running terminal emulation software. Many companies desire to make this content accessible to customers through the Internet or to employees through an "intranet" which has a Web-like structure and user interface.
Conventional approaches for providing such access typically use conversion/translation techniques that employ emulation software resident at an intermediate Web server. Additional code typically executes on top of the emulation software that is capable of establishing a session from the intermediate server to a host and converting emulation screen output/input into a format understood by the browser, such as HTML files, Java GUI applets, or ActiveX controls. The intermediate code typically employs a private protocol to control the exchange of data between the server and browser in the converted format.
There are several potential problems with this technique. For example, use of an intermediate server may make it difficult to navigate a host session as if it were an integral part of a browser environment. The state of the host session typically is not maintained in real time on the browser, so a user may respond to an inappropriate screen. In addition, when a Web user leaves a session to surf other Web pages and comes back, the session may be disconnected or disrupted; indeed, many conventional Web-based host access solutions restrict users from leaving a session to access other Web pages, and may force a session disconnection if a user does so. Such restriction tends to be disruptive and can limit the potential flexibility offered by a Web-based solution.